Re: [PATCH 4/9] spi: sun4i: add DMA support

From: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: "Emilio López" <emilio-0Z03zUJReD5OxF6Tv1QG9Q@public.gmane.org>
Cc: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org,
	Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Ian Campbell
	<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
	Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
	Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>,
	Maxime Ripard
	<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 4/9] spi: sun4i: add DMA support
Date: Thu, 20 Aug 2015 11:58:50 -0700	[thread overview]
Message-ID: <20150820185850.GQ12027@sirena.org.uk> (raw)
In-Reply-To: <ccf776869b0d7fe2c78bcc41d6cd1896bf732296.1440080122.git.hramrach-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

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On Thu, Aug 20, 2015 at 02:19:46PM -0000, Emilio López wrote:

> -	sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> +	if (sun4i_spi_can_dma(master, spi, tfr) && desc_rx) {
> +		/* The receive transfer should be the last one to finish */
> +		dma_wait_for_async_tx(desc_rx);

What if it's a transmit only transfer?  We'll fall over to this...

> +	} else {
> +		sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> +	}

...which manually reads data from the FIFO which doesn't seem like what
we want, won't it conflict with the DMA?

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